Well drilling mud and process



Patented June 26, i fi i'fifitSJlC ii WELL DRKLEENG AND ZPIRDSESS Everett P. Partridge, heaven Pa assignor to Hall Laboratories, Hide Pittsburgh, Fa a corpora tion oi 'iFennsylvania No Drawing. Application Eannary 1%, recs. derial No state? It Claims. (\Cl. 252-35) This application is a continuation-in-part of my copending application, Serial No. 463,816, filed October 29, 1942, which in turn was a continuation-in-part of my application, Serial No. 351,983, filed August 9, 1940.

This invention relates generally to the drilling of oil and similar wells and to a drilling mud for use in the process. In drilling oil wells, for example, it is customary to employ a mud or fluid which serves various purposes which are well known. The drilling mud is circulated from a sump above the ground down through the bore, around the drilling tool where it picks up the chips formed by the drill, and then up the bore to screens where the chips are removed, and to the sump from which the mud is again. circulated through the bore. The mud also serves to lubricate the drill pipe, to seal the wall of the bore, and to provide a hydrostatic head which prevents the well from blowing out, in case high formation pressures are encountered.

In order to increase the weight of the drilling mud, it has been customary in the past to add weighting material, such, for example, as barite or hematite. While these or other materials are satisfactory from the standpoint of increasing the weight of the mud, they increase the viscosity of the mud, so that it becomes more difficult to pump. If it is attempted to increase the weight of the mud by increasing the proportion of clay to water either with or without the addition of lated downward through the bore, it is subjected to increasing temeratures which may exceed 26%? F. The increase in temperature affects the properties of the mud adversely to a greater or less extent and tends to destroy the effects of the dissolved metaphosphate by causing reversion to the ineffective orthophosphate,,and likewise, to

destroy the effect of the dissolved pyrophosphate both by precipitation as highly insoluble calcium or magnesium pyrophosphate and by reversion to I the ineffective orthophosphate.

While the loss of the metaphosphate or pyrophosphate during circulation through the bore may be made up by further addition of these agents at the surface of the ground, it is difiicult to control the conditionin of' the mud at the surface so that it will exhibit optimum properties at increased temperatures deep in the bore, without at the same time overtreating with respect to surface conditions and hastening the approach of the time when the mud will no longer respond having a molar ratio of alkali-metal oxide to weighting agents, the viscosity likewise is increased too much.

It has been proposed heretofore to increase the fluidity of the mud by adding thereto a solution of rapidly soluble sodium hexametaphosphate or sodium pyrophosphate. These phosphates have the property of dispersing or deflccculating the mud and making it more fluid. In this manner,

when the ratio of solids to water is increased,

or weighting materials are added to the mud, the increased viscosity which would result therefrom may be overcome by the use of the rapidly soluble metaphosphate or pyrog'ihosphate.

The use of the rapidly water-soluble metaphosphate or pyrophosphate has resulted in considerable improvement in drilling muds, but is open P205 less than 1:1, are introduced into the mud and are circulated with the mud down the here These slowly soluble particles dissolve continuously in the mud to maintain the desired properties in it and particularly to maintain the mud in a suitably fluid condition.

The term molecularly dehydrated phosphatef.

is recognized as describing those phosphate com pounds which may be degarded as derived from phosphoric acid or monobasicor clibasic orthophosphate or mixtures thereof by removal of water of constitution.

Slowly soluble molecularly dehydrated alkalimetal phosphate glass having a molar ratio of alkali-metal oxide to P20 less than ltl may he formed from the fusion of a monobasic orthophosphate with an excess of phosphoric acid as illustrated by the reaction:

The product Na1oP1zOa5 may be described as 5NazO.6Pz05, which has a molar ratio of Nazi) to P205 ofabout 0.8:1. The melt is rapidly chilled in order to produce the product in glassy form. By a similar reaction, the corresponding slowly soluble molecularly dehydrated potassium phosphate glass having a molar ratio of K20 to Plot of less than 1:1 ,mavbe produced.

Commercially, the slowly soluble molecularly dehydrated alkali-metal phosphate glasses may be made from phosphoric acid and a convenient compound of the desired alkali-metal such as the oxide, hydroxide, carbonate or chloride, sufficient heat being applied to drive off substantially all of the water and in the case of metal salts such as the carbonate or chloride to drive off the acidic constituent, such as carbon dioxide or hydrogen chloride. Thus, for example, I may produce a slowly soluble molecularly dehydrated sodium phosphate glass having a molar ratio of Na20 to P205 of approximately 0.6:1.0 by the reaction of three mols of sodium carbonatewith ten mols of Thus .100 grams of sodium metaphosphate glass commonly known as sodium hexametaphosphate ground to pass a 200-mesh screen when mixed with one liter of water will dissolve in less than. one minute, thereby producing a concentration of 100,000 P. P. M. Even higher concentrations are easily and almost instantaneously obtained. On the other hand, when 100 grams of molecularly dehydrated sodium phosphate glass or the mol per cent composition 45Na20.55P205 is mixed with one liter of water, an hour is required for it to dissolve. phosphate glass is less than that of the sodium hexametaphosphate under comparable conphosphoric acid, according to the following equaditions. tion: The molecularly dehydratedalkali-metal phosphate glasses having a molar ratio of alkali-metal gg 5014 +15H2O +3Co2 oxide to P205 less than 1:1 may be referred to for convenience as "acid phosphate glasses." The me t s quickly chilled, in Ord o pro- These acid phosphate glasses, while being suflld ce t e P d in glassy form- The Product ciently soluble in a previously untreated mudto s M y be Written as 3Na2O',5P2O5- This materially lower the viscosity of the mud, never- Drodllct has a mOl P t Composition 0f theless are of an entirely different and lower or- NazO and 62.5 P2O5,"Which is a o ar r o of der of solubility than the rapidly soluble glassy Naz0 to P205 of 06:10. The corresponding posodium metaphosphate commonly'known as sotassium phosphate glass may be made in a simil dium hexametaphospliate or Grahams salt. The manner 0 asse c ta ing t o or more difrate of solution of the acid phosphate glasses used ere a a metals maybe made om phosaccording to my invention is only a small fracph ri a id and w or more p nds on i tion of the rate of solution of sodium hexametaing difierent alkali-metals. Thus I can make sophosphate. The term "slowly soluble" is used in -P tassium glasses, S -lithium glasses, the claims to define such molecularly dehydrated potassium-lithium glasses or sodium-potassiumphosphate glass. th lasses in which the molar ratio of total The efiect on the viscosity and gel strength of a ie o e to Phosphorous DentOXide i well drilling mud produced by the addition to 1.658 than 111, Preferably from 0-511 110 .35 the mud of various materials is shown in Table other po s of alkali-metals y be I. In carrying out the tests, a mud was made up used in place of the carbonates and the ratios of to tai 10% of clay, 20% of ground barite, a1kali-metal and phosphorus in the starting and 3% of bentonite, and was aged with stirring. mixture may be varied so that the phosphate To a 2000-gram' portion of the aged mud was glass will have a molar ratio of alkali-metal oxide 40 added 3 grams of th material to be tested, ground to P505 of less than 1:1. It is preferred that this t pass a, 2 creen. The sample was then ratio be between about 0.521 and 0.9:1 and more thoroughly mixed and allowed to stand 0.5 hour, p c a y a e ra o be abou 0.611- As th when the viscosity and 5-minute gel strength were ratio of alkali-metal oxide to P205 is lowered; the determined by means of MeMiehael viscosimphosphate glass becomes more hydroscopic and eter. The sample was then allowed to stand more diflicult to manufacture'and handle and ac overnight, approximately 15 hours, after which rd n y in Commercial p ce it is usually n it was mixed thoroughly, and the viscosity and advisable to p y P p e glasses having a gel strength were again determined. The sample ratio of alkali-metal oxide to P205 lower than wa then heated t -80 C. for .two hours and alabout 0.521. lowed to cool and stand overnight, after which In place of adding to the drilling mud Slowly the viscosity and gel strength were again desoluble'alkali-metal phosphatev glass containing termined. The original mud with no addition of a plurality of alkali-metals, I may add to the mud treating chemical had a viscosity of 64 poises at a mechanical mixture of two or more different 20 R. P. M., and a 5-minute gel strength of341 alkali-metal phosphate glasses, the mixture havon an arbitrary scale.

TABLE I Synthetic mud Mummies ethane N0 Composition of treating material mol per cent 2hr at 2 hr at 0.5 Over- 5 d 0.5 Over- 0 Cito night overnight night overnight iqtfii'if iricii fit iaimainstaysnest: 53.5 3.5 55.5 3% 53 i3 1 46N810,55P10l phospha e ass) 9 o 21 65 '77 111 2 40N81O,60P1O| acid ph sphat glass) 56 20 7 13 ing a molar ratio of alkali-metal oxide to P205 of less than 1, preferably between about 0.5:1 and It will be seen that the acid phosphate glasses numbered 1 and 2 materially reduce the viscosity of the mud and furthermore that theyare con;

Thus the rate of solution of the acid TABLE; H

Formation mad grams of mud, with vigorous mixing for live minutes. The viscosity of the mixture was then determined by immersing the. spindle of a Brookfield viscosimeter in the mud and reading the viscosity 1% minutes after mixing was stopped. Similar measurements were made after the mud had stood for an hour, after it had stood over- Viscosity, pulses 5-minute gel strength arbitrary units Composition of treating materiel we. per cent g w, lliolgrat '5 Q ogfiohrat mg overnight mghH' overnight Mud treated in the field"... it. 15.5 17. 12 71 72 50Na1O.50Pi0i(sodium mctaphosphateglass) 1L5 12.5 10.5 57 53 (i4 5 dfiaNhzoiifipaos (acid phosphate giass)....... 9.5 9.5 ll.5 44 4:; 54

In thi case, as the mud was already satisfactorily dispersed or defiocculated, the further decreases in viscosity were not as pronounced a in the case of the synthetic mud. Nevertheless, it is noteworthy that significantly greater effects were shown by the acid phosphate glass than by the sodium metaphosphate glass, particularly, after heating. 1 I

The effect on the viscosity of well drilling mud night, and after it had then been heated for two hours at 80 C. and had been allowed to cool to room temperatur by standing overnight again. In each case the mud was stirred for five minutes before the viscosity reading was taken 1 /2 minutes after the cessation of stirring.

All readin s were made with a No. 3 spindle on the Brookfield viscosimeter rotating at 12 R. P. M., and the readings were converted to poises.

TABLE 111 Synthetic mud C m .i i n l n r After 0 2 hr. at

N820 K Lno P 05 5 min. 1 hr o. to

stirring g overnight No treatlng 67. (i 69. 0

material.

1.1 1 14.0 19.8 32.2 1 2 29.6 18.0 21.8 43.8 1 l l 6 40. 4 l2. 4 l2. 8 25. 6 1 l :j 4 22. 6 12.0 14. 8 23.0 2 2 7 26.4 11.4 12.6 20.0 i 1 4 51.2 45.8 23.8 16.2

dure was followed as in the work which provided the data for Table I. The various glasses were made by mixing the proper amounts of the respective alkali-metal carbonates and of phosphoric acid, heating the mixture for abouthalf an hour at approximately 900 C. to drive off water and carbon dioxide, and quenching'the melt between metal surfacesto produce a clear glass. v A portion of each glass was powdered. This powdered material was used in testing the ability of the glass to reduce the viscosity of a drillin mud mixture.

The mud was made up mately 9.5% of Baroco" clay, used in drilling mud, 19.5% or g mercial weighting agent for drilling mud consisting essentially of barium sulphate, and 0.95% of Aquagel," a. commercial bentonite used in dr lling mud, the remainder of the mixture being water. Each test was conducted by adding 3 grams oi powdered acid phosphate glass to 2000 to contain'approxia commercial clay It will be noted from the figures in Table III that each of the five acid phosphate glasses (Nos.

3, 4, 5, 6 and '7) decreases the viscosity of thejmud very markedly. Four of the five proved more ef-,

fective in holding down the viscosity of the mud after it had been heated than did the approximately neutral relatively soluble commercial sodium phosphate glass (No. 2).

In carrying out the process of conditioning well drilling mud by means of the slowly soluble acid phosphate glasses, I prefer to maintain a reserve of undissolved solid particles of the treating material in the mud as it is circulated throughout the cycle, adding more of the treating material to the mud continuously or at intervals to make up the unavoidable losses, and controlling this makeup by testing the properties of the mud at intervals. 7 The test methods heretofore employed are suitable in which the viscosity of the mud is Baroid, a commeasured in an approximate manner by the time of eiliux of a given quantity from a Marsh funnel. or more precisely by a viscosimeter. The tests should preferably be carried out with the mud held at approximately the maximum temperature in the bore hole, although an experienced operator may be able to maintain satisfactory control by "testing the mud at its temperature at the surface or th ground.

'Initial adjustment of a mud to the desired level of viscosity may require the addition at the start of a greater amount of acid phosphate glass than would have been necessary it rapidly soluble soscribed is the automatic response to increase in temperature as the mud circulates down the bore. When the rapidly soluble molecularly dehydrated phosphates are introduced into and dissolve in the mud at the surface of the ground, the effect of increase in temperature as the muddescends the bore is to accelerate the loss of treating chemical by precipitation or revision or both undesirable reactions. In contrast, when finely divided slowly soluble acid phosphate glasses are introduced into the mud, only a limited amount goes into solution.

As the temperature increases during passage downthe bore, there is an increase in the rate of loss of the effective chemical in solution, but this is offset by the increased rate at which the solid particles of the treating material dissolve to supply fresh chemical to the solution.

Another advantage of the slowly soluble acid phosphate glasses is the fact that they can be stored and handled in humid atmospheres with less tendency toward caking than is exhibited by the readily soluble molecularly dehydrated phosphates'heretofore employed.

It will be apparent to one skilled in the art of dispersing or defiocculating clays, pigments, fillers, and finely divided oxides, salts, and mineral matter in'general that the slowly soluble acid phosphate glasses may be utilized to advantage as dispersing or deflocculating agents in many operations other than the conditioning of mud in the drilling of bore holes.

The invention is not limited to the preferred materials or preferred manner of practicing the method but-may be otherwise embodied or practiced within the scope of the following claims.

I claim: 4

1. Well drilling mud comprising an aqueous dispersion of clay and solid particles of slowly soluble 49 dium and potassium, said phosphate glass having sodium phosphate glass having a molar ratio 01' NAzO to P205 between about 0.5:1 and 0.9:1.

2. Well drilling mud comprising an aqueous dispersion of clay and solid particles of slowly soluble potassium phosphate glass having a molar ratio of K20 to P205 between about 0.5:1 and 0.9:1.

3. Well drilling mud comprising an aqueous dispersion of clay and solid particles or slowly soluble molecularly dehydrated alkali-metal phosphate glass having a. molar ratio of alkali-metal oxide to P205 between about 0.5:1 and 0.9:1.

4'. Well drilling mud comprising an aqueous dispersion of clay and solid particles of slowly soluble molecularly dehydrated alkali-metal phosphate glass having a molar ratio of alkali-metal oxide to P205 of about 0.6:1.

5. The process of controlling the viscosity oi! well drilling mud, which comprises adding thereto solid particles of slowly soluble molecularly dehydrated alkali-metal phosphate glass having a molar ratio of alkali-metal oxide to P205 between about 0.5:1 and 0.9:.1.

6. A dispersion of finely divided mineral matter in an aqueous medium, said dispersion containing an eiiective amount of solid particles of slowly soluble molecularly dehydrated alkali-metal phosphate glass having a molar ratio of alkali-metal oxide to P205 between about 0.521 and 0.9: l which acts to disperse or deflocculate the mineral mattei'.

7. Well drilling mud comprising an aqueous dispension of clay and solid particles of slowly soluble alkali-metal phosphate glass containing a plural ity of alkali metals, said phosphate glass having a molar ratio of alkali-metal oxides to P205 between about 0.521 and 0.9:1.

8. Well drilling mud comprising an aqueous dispersion of clay and solid particles of slowly soluble alkali-metal phosphate glass containing both soa molar ratio of alkali-metal tween about 0.5:1 and 0.9:1.

9. Well drilling mud comprising an aqueous dispersion of clay and solid particles of a mechanical mixture of alkali-metal phosphate glasses containing difierent alkali metals, said mixture having a, molar ratio of alkali-metal oxides to P205 between about 05:1 and 0.9: 1.

10. A material adapted to control the viscosity aqueous well drilling mud, said material comprising slowly soluble alkali-metal phosphate glass containing a plurality of alkali-metals, said phosphate glass having a molar ratio of alkalioxides to P205 bemetal oxides to P205 between about 0.5:1-and EVERETT P. PARTRIDGE.

v CERTIFICATEOF CORRECTION; Patent No. 2,379,100. June 26, 191

EVERETT P. PARTRIDGE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, sec 0nd column, line 56,10r "degarded" read --regarded page 14., first column, line 25; for "revision" read "reversion"; and second column, line hB, claim 9, for "05:1" read --O.5:l--; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

} Signed and. sealed this 25th day of September, A. D. l9h5.

Leslie Frazer (Seel) F irst Assistant Commissioner of Patents. 

